Document WO03100185 discloses a steel beam arranged to serve together with concrete as a bearing composite structure for various slab systems, the composite structure comprising a base plate and two web parts arranged side by side at a distance from each other and joined at first ends by means of a horizontal top part. The base plate, web parts and horizontal top part are arranged to form a space that can be filled with concrete. At least one web part is made of a plate part formed of two longitudinal parts of the beam that are at an angle to each other. The plate part is fastened to the base plate and top part in such a manner that the lower part of the web part is at an angle to the base plate and the upper part is substantially perpendicular to the base plate.
Document WO03100187 discloses a steel beam that is arranged to serve together with concrete as a bearing composite structure for various slab systems, the composite structure comprising a base plate and two web parts arranged side by side at a distance from each other and joined at first ends of the web parts by means of a horizontal top part, whereby the base plate, web parts and horizontal top part are arranged to form a space that can be filled with concrete. One web part is in a manner known per se made slanted relative to the base plate and a corbel flange extending from it and equipped with openings. The other web part is, in turn, made substantially perpendicular to the base plate and has no openings.
A problem with the above mentioned structures is that when the steel beam is filled with concrete for forming a bearing composite structure, the resulting beam is very heavy. It is also required to give the concrete sufficient time to cure, which has to be taken into account in the construction schedule.